This is something you see often at low stakes online and live tournaments...

Math tells us that we want to 3b more rather then flat vs a large RFI due to getting worse odds to enter the pot, but in practicality we don't want to do this because this is usually a fairly strong range (maybe not nutted) of hands like AK/AQ/QQ-99 etc...

Of course, the obvious flaws in this sizing tell is that V becomes face up and we now attack V's smaller RFI sizing range, but what about when facing a 4x+ and holding hands like TT/99 or AQ/AJ/KQ when we face these large sizings?

The odds of flopping something drastically decrease because V often holds a lot of our outs, so we c/f a lot on flop and lose a larger pot, and when we do hit there are reverse implied odds considerations... This is problematic at 50bb< where you cannot no longer nutpeddle against an assumed rec, 3b sucks because of no FE, and losing blinds become more valuable...

Wondering on your thoughts... is it wise to just fold?

Well, theory says you should fold more to bigger sizing. If they are very nutty in their openings, hitting a speculative hand has more value, since they are more likely to stack off when holding an overpair.

Reality is that most of the time this is just a very bad player, so playing pots with them is strongly incentivized, and keeping the SPR low is good as well, so I'd mostly be flatting some big hands here, and 3!ing far less.

When someone opens big, they are usually not folding to a 3!. So I would almost always 3! QQ+. It might be fine to flat JJ/AK is you are reasonably deep and do not want to gii with those hands. It depends on reads and how the person is playing whether the big size indicates strength and how much strength it indicates.